1. Field of the Invention
This invention relates generally to a packaging tray for shipping sensitive glass plates which have extremely low tolerances for receiving impurities on the plate surface. The plate is to be utilized as a microoptic device; therefore, one side of the plate surface must be kept as free from impurities as possible.
2. Description of the Prior Art
Several packaging devices have been shown in the prior art constructed of plastic materials for use in protecting photographic slides and the like which have been unacceptable for shipping impurity sensitive plates due to vapor transmission and the vapor pressure of the plastic material which deposits impurities from the package itself onto the surface of the sensitive plate. Metal packages have been shown in the prior art but are unacceptable since any dimensional variation between the glass plate and the package caused relative movement in the package during shipping and handling, producing quantities of microscopic particles on the sensitive plate. Also particles from the raw cut peripheral edges of the metal package were deposited on the sensitive plate during handling, wrapping and unwrapping of the plate. Applicant's invention overcomes these problems by providing a sufficiently ductile but non-resilient package having a ridge and groove shaped sidewall structure for supporting and retaining a sensitive plate, each wall edge being folded back to prevent microscopic flakes along the cut edge of the sidewall from being received within the tray itself. The ductile material and sidewall contour minimize plate edge chipping along the contacting peripheral plate edge. Plate-tray relative movement is minimized by pressing the ductile package wall and the plate edge together embedding the plate edge in the package wall. The folded sidewall also increases the structural integrity of the package. Additionally the use of aluminum foil to cover and seal the package prevents further flaking and allows a chemical to be deposited and sealed within the package itself to enhance the wetability of subsequent photo-sensitive coating on the plate surface.